Turn IFUNC symbols from shared libraries into normal FUNC symbols

Turn IFUNC symbols from shared libraries into normal FUNC symbols

Turn IFUNC symbols from shared libraries into normal FUNC symbols when
we are resolving symbol references, instead of when we are writing out
the symbol table.

	PR gold/18886
	* resolve.cc (Symbol::override_base): Turn IFUNC symbols from
	shared libraries into normal FUNC symbols.
	* symtab.cc (Symbol_table::sized_write_symbol): Assert IFUNC
	symbols aren't from shared libraries.